Soldering is a general technique for surface mounting electronic components on the surface of a printed circuit board. In performing soldering, flux is generally used for the purpose of achieving sufficient solderability by removing an oxide film from the solder and the parent material surface or preventing the solder and the parent material surface from reoxidation. However, flux is corrosive, and flux residues decrease the quality of a printed circuit board. Therefore, in some cases, flux residues are removed by cleaning.
Heretofore, rosin-based flux (rosin flux) has widely been used in solder joints on surface-mounted components, and rosin flux residues would be cleaned off with a halogenated hydrocarbon such as so-called chlorofluorocarbon. However, because halogenated hydrocarbons are extremely harmful to the environment, the use thereof has been restricted. For this reason, various cleaners for removing rosin flux residues have been considered as a replacement for halogenated hydrocarbons, etc. For example, a cleaner containing, for example, polyoxyalkylene alkyl ether-based halogen-free organic solvent is suggested as having reduced ignition risk, reduced environmental effects, as well as an excellent property of dissolving rosin flux residues (see Patent Literature 1 to 3).
As a means to address environmental issues, cleaning with water in place of halogenated hydrocarbons has been considered. Fluxes that can be cleaned off with water include a water-soluble flux, in which an activator, a solvent, etc., are added to a polyether-based resin, etc., rather than hydrophobic fluxes, such as rosin fluxes. Water-soluble flux residues are hygroscopic, and must therefore be cleaned off. Such a feature of water-soluble flux residues differs from the feature of rosin flux residues, i.e., rosin flux residues do not necessarily need to be cleaned off. As such, the water-soluble flux residues are generally cleaned off with water; however, the cleaning can be insufficient.
In view of the above, as a cleaner for removing water-soluble flux residues, the use of the cleaners of, for example, Patent Literature 1-3, can be considered. However, these cleaners have not been studied for the purpose of removing water-soluble flux residues. In addition, it was difficult for the above-mentioned rosin flux cleaners to sufficiently clean off water-soluble flux residues, which have properties different from those of rosin flux residues.